Fast and reliable data carrier detection by a cable modem in a cable television plant

Abstract

Apparatus, methods, and computer program products for detecting or locating a viable data carrier in a downstream channel by a cable modem. Potential channels for data carriers can be eliminated quickly by going through a “screening” process, i.e., the first constellation diagram match, thereby preventing those potential channels from going through a significantly more time-consuming second constellation match. The determination of whether the signal in the potential channel is modulated according to the first particular modulation scheme is done rapidly and only potential channels containing a signal likely to be modulated according to the second particular modulation scheme are examined for the second determination step.

1. An apparatus of detecting a data carrier in a downstream band in a cable plant, the apparatus comprising:
 (a) means for selecting a potential data carrier from within the downstream band; 
 (b) means for determining whether the potential data carrier contains a signal modulated according to a first modulation scheme wherein the first modulation scheme is not a default modulation scheme used on signals in the downstream band; 
 (c) means for determining whether the potential data carrier contains a signal that is apparently not modulated according to the first modulation scheme; and 
 (d) means for determining whether the potential data carrier contains a signal modulated according to a second modulation scheme wherein the second modulation scheme is the default modulation scheme used on signals in the downstream band. 
 
   
   
     2. The apparatus of  claim 1  wherein the means for selecting a potential data carrier further comprises means for determining a data carrier most recently used by the cable modem. 
   
   
     3. The apparatus of  claim 1  wherein the first modulation scheme is QPSK and the second modulation scheme is one of QAM64 and QAM256. 
   
   
     4. The apparatus of  claim 1  wherein the means for determining whether the potential data carrier contains a signal modulated according to a first modulation scheme further comprises means for matching a signal from the potential data carrier against a constellation corresponding to the first modulation scheme. 
   
   
     5. The apparatus of  claim 1  wherein the means for determining whether the potential data carrier contains a signal modulated according to a second modulation scheme further comprises means for determining whether a signal-to-noise ratio associated with the potential data carrier when demodulated according to the first modulation scheme is less than a first predetermined signal-to-noise ratio in which case the potential data carrier is not accepted. 
   
   
     6. The apparatus of  claim 1  wherein the means for determining whether the potential data carrier contains a signal modulated according to a second modulation scheme further comprises means for matching a signal from the potential data carrier against a constellation corresponding to the second modulation scheme. 
   
   
     7. The apparatus of  claim 1  further comprising means for determining whether a signal-to-noise ratio for the second modulation scheme associated with the potential data carrier is greater than a second predetermined signal-to-noise ratio. 
   
   
     8. The apparatus of  claim 1  further comprising means for configuring a receiver chip in the cable modem to detect a QPSK signal before step (b) and then reconfiguring the receiver chip to detect one of a QAM64 signal and a QAM256 signal before step (c). 
   
   
     9. An apparatus of locating a correct downstream channel for use by a cable modem in a cable plant, the apparatus comprising:
 (a) means for, from a plurality of unexamined downstream frequency channels, selecting an unexamined downstream frequency channel; 
 (b) means for determining whether the unexamined downstream frequency channel does not have a first modulation-type signal and a signal-to-noise ratio higher than a first predetermined threshold signal-to-noise ratio; 
 (c) means for determining whether the unexamined downstream frequency channel has a signal-to-noise ratio higher than the first predetermined threshold signal-to-noise ratio; 
 (d) means for returning to step (a); 
 (e) means for determining whether the unexamined downstream frequency channel has a second modulation-type signal and a signal-to-noise ratio less than a second threshold signal-to-noise ratio; 
 (f) means for determining whether the unexamined downstream frequency channel has a signal-to-noise ratio less than the second threshold signal-to-noise ratio; 
 (g) means for returning to step (a); and 
 (h) means for repeating steps (a) to (g) until an unexamined downstream frequency channel is selected that has a second modulation-type signal and signal-to-noise ratio at least as high as the second threshold signal-to-noise ratio. 
 
   
   
     10. The apparatus of  claim 9  wherein the means for selecting an unexamined downstream frequency channel further comprises means for determining a channel most recently used by the cable modem for previous communication in the cable plant. 
   
   
     11. The apparatus of  claim 9  wherein the means for selecting an unexamined downstream frequency channel further comprises means for selecting a frequency channel from a plurality of frequency plans. 
   
   
     12. The apparatus of  claim 9  wherein the means for determining whether the unexamined downstream frequency channel does not have a first modulation-type signal and a signal-to-noise ratio higher than a first predetermined threshold signal-to-noise ratio further comprises means for matching a signal in the unexamined downstream frequency channel against a constellation corresponding to a first modulation scheme. 
   
   
     13. The apparatus of  claim 12  wherein the first modulation scheme is QPSK. 
   
   
     14. The apparatus of  claim 9  wherein the means for determining whether the unexamined downstream frequency channel has a second modulation-type signal and a signal-to-noise ratio less than a second threshold signal-to-noise ratio further comprises means for matching a signal in the unexamined downstream frequency channel against a constellation corresponding to a second modulation scheme. 
   
   
     15. The apparatus of  claim 14  wherein the second modulation scheme is one of QAM64 and QAM256. 
   
   
     16. The apparatus of  claim 9  wherein the second modulation-type signal is one of a QAM64 and QAM256 modulated signal. 
   
   
     17. An apparatus of detecting a data carrier in a downstream channel in a cable plant, the apparatus comprising:
 (a) means for selecting a potential data carrier; 
 (b) means for attempting to analyze the potential data carrier for a particular modulation scheme, wherein the modulation scheme is not a default modulation scheme used on signals in the downstream band; 
 (c) means for determining whether a signal-to-noise ratio in the potential data carrier when analyzed for the particular modulation scheme is greater than a defined threshold signal-to-noise ratio; 
 (d) means for determining whether the signal-to-noise ratio is greater than the defined threshold signal-to-noise ratio; and 
 (e) means for abandoning the potential data carrier from further consideration and selecting a different data carrier for further analysis. 
 
   
   
     18. The apparatus of  claim 17  further comprising means for selecting the potential data carrier for further analysis for determining whether the potential data carrier is a viable data carrier if the signal-to-noise ratio is below the defined threshold signal-to-noise ratio. 
   
   
     19. The apparatus of  claim 18  further comprising:
 (f) means for attempting to analyze the potential data carrier for an expected modulation scheme; 
 (g) means for determining whether a signal-to-noise ratio in the potential data carrier when analyzed for the expected modulation scheme is greater than a second defined threshold signal-to-noise ratio; 
 (h) means for determining whether the signal-to-noise ratio is greater than the second defined threshold signal-to-noise ratio; and 
 (i) means for using the potential data carrier as a viable data carrier. 
 
   
   
     20. The apparatus of  claim 17  wherein the particular modulation scheme is QPSK. 
   
   
     21. An apparatus of detecting a data carrier in a downstream band in a cable plant, the apparatus comprising:
 (a) means for selecting a potential data carrier from within the downstream band; 
 (b) means for determining that the potential data carrier does not contain a signal modulated according to a first modulation scheme wherein the first modulation scheme is not a default modulation scheme used on signals in the downstream band; and 
 (c) means for determining that the potential data carrier contains a signal modulated according to a second modulation scheme wherein the second modulation scheme is the default modulation scheme used on signals in the downstream band by concluding that the potential data carrier contains a signal that is apparently not modulated according to the first modulation scheme. 
 
   
   
     22. A cable modem comprising:
 a CPU (central processing unit); 
 a memory; and 
 instructions for detecting a data carrier in a downstream band in a cable plant, the instructions comprising:
 (a) instructions for selecting a potential data carrier from within the downstream band; 
 (b) instructions for determining whether the potential data carrier contains a signal modulated according to a first modulation scheme wherein the first modulation scheme is not a default modulation scheme used on signals in the downstream band; 
 (c) instructions for determining whether the potential data carrier contains a signal that is apparently not modulated according to the first modulation scheme; and 
 (d) instructions for determining whether the potential data carrier contains a signal modulated according to a second modulation scheme wherein the second modulation scheme is the default modulation scheme used on signals in the downstream band. 
 
 
   
   
     23. The cable modem of  claim 22  wherein the instructions for selecting a potential data carrier further comprise instructions for determining a data carrier most recently used by the cable modem. 
   
   
     24. The cable modem of  claim 22  wherein the first modulation scheme is QPSK and the second modulation scheme is one of QAM64 and QAM256. 
   
   
     25. The cable modem of  claim 22  wherein the instructions for determining whether the potential data carrier contains a signal modulated according to a first modulation scheme further comprise instructions for matching a signal from the potential data carrier against a constellation corresponding to the first modulation scheme. 
   
   
     26. The cable modem of  claim 22  wherein the instructions for determining whether the potential data carrier contains a signal modulated according to a second modulation scheme further comprise instructions for determining whether a signal-to-noise ratio associated with the potential data carrier when demodulated according to the first modulation scheme is less than a first predetermined signal-to-noise ratio in which case the potential data carrier is not accepted. 
   
   
     27. The cable modem of  claim 22  wherein the instructions for determining whether the potential data carrier contains a signal modulated according to a second modulation scheme further comprise instructions for matching a signal from the potential data carrier against a constellation corresponding to the second modulation scheme. 
   
   
     28. The cable modem of  claim 22  further comprising instructions for determining whether a signal-to-noise ratio for the second modulation scheme associated with the potential data carrier is greater than a second predetermined signal-to-noise ratio. 
   
   
     29. The cable modem of  claim 22  further comprising instructions for configuring a receiver chip in the cable modem to detect a QPSK signal before step (b) and then reconfiguring the receiver chip to detect one of a QAM64 signal and a QAM256 signal before step (c). 
   
   
     30. A cable modem comprising:
 a CPU (central processing unit); 
 a memory; and 
 instructions for detecting a data carrier in a downstream channel for use by a cable modem in a cable plant, the instructions comprising:
 (a) instructions for, from a plurality of unexamined downstream frequency channels, selecting an unexamined downstream frequency channel; 
 (b) instructions for determining whether the unexamined downstream frequency channel does not have a first modulation-type signal and a signal-to-noise ratio higher than a first predetermined threshold signal-to-noise ratio; 
 (c) instructions for determining whether the unexamined downstream frequency channel does have a signal-to-noise ratio higher than the first predetermined threshold signal-to-noise ratio; 
 (d) instructions for returning to step (a); 
 (e) instructions for determining whether the unexamined downstream frequency channel has a second modulation-type signal and a signal-to-noise ratio less than a second threshold signal-to-noise ratio; 
 (f) instructions for determining whether the unexamined downstream frequency channel has a signal-to-noise ratio less than the second threshold signal-to-noise ratio; 
 (g) instructions for returning to step (a); and 
 (f) instructions for repeating steps (a) to (g) until an unexamined downstream frequency channel is selected that has a second modulation-type signal and signal-to-noise ratio at least as high as the second threshold signal-to-noise ratio. 
 
 
   
   
     31. The cable modem of  claim 30  wherein the instructions for selecting an unexamined downstream frequency channel further comprise instructions for determining a channel most recently used by the cable modem for previous communication in the cable plant. 
   
   
     32. The cable modem of  claim 30  wherein the instructions for selecting an unexamined downstream frequency channel further comprise instructions for selecting a frequency channel from a plurality of frequency plans. 
   
   
     33. The cable modem of  claim 30  wherein the instructions for determining whether the unexamined downstream frequency channel does not have a first modulation-type signal and a signal-to-noise ratio higher than a first predetermined threshold signal-to-noise ratio further comprise instructions for matching a signal in the unexamined downstream frequency channel against a constellation corresponding to a first modulation scheme. 
   
   
     34. The cable modem of  claim 33  wherein the first modulation scheme is QPSK. 
   
   
     35. The cable modem of  claim 30  wherein the instructions for determining whether the unexamined downstream frequency channel has a second modulation-type signal and a signal-to-noise ratio less than a second threshold signal-to-noise ratio further comprise instructions for matching a signal in the unexamined downstream frequency channel against a constellation corresponding to a second modulation scheme. 
   
   
     36. The cable modem of  claim 35  wherein the second modulation scheme is one of QAM64 and QAM256. 
   
   
     37. The cable modem of  claim 30  wherein the second modulation-type signal is one of a QAM64 and QAM256 modulated signal. 
   
   
     38. A cable modem comprising:
 a CPU (central processing unit); 
 a memory; and 
 instructions for detecting a data carrier in a downstream channel in a cable plant, the instructions comprising:
 (a) instructions for selecting a potential data carrier; 
 (b) instructions for attempting to analyze the potential data carrier for a particular modulation scheme, wherein the modulation scheme is not a default modulation scheme used on signals in the downstream band; 
 (c) instructions for determining whether a signal-to-noise ratio in the potential data carrier when analyzed for the particular modulation scheme is greater than a defined threshold signal-to-noise ratio; 
 (d) instructions for determining whether the signal-to-noise ratio is greater than the defined threshold signal-to-noise ratio; and 
 (e) instructions for abandoning the potential data carrier from further consideration and selecting a different data carrier for further analysis. 
 
 
   
   
     39. The cable modem of  claim 38  wherein the instructions further comprise instructions for selecting the potential data carrier for further analysis for determining whether the potential data carrier is a viable data carrier if the signal-to-noise ratio is below the defined threshold signal-to-noise ratio. 
   
   
     40. The cable modem of  claim 39  further comprising:
 (f) instructions for attempting to analyze the potential data carrier for an expected modulation scheme; 
 (g) instructions for determining whether a signal-to-noise ratio in the potential data carrier when analyzed for the expected modulation scheme is greater than a second defined threshold signal-to-noise ratio; 
 (h) instructions for determining whether the signal-to-noise ratio is greater than the second defined threshold signal-to-noise ratio; and 
 (i) instructions for using the potential data carrier as a viable data carrier. 
 
   
   
     41. The cable modem of  claim 38  wherein the particular modulation scheme is QPSK. 
   
   
     42. A cable modem comprising:
 a CPU (central processing unit); 
 a memory; and 
 instructions for detecting a data carrier in a downstream band in a cable plant, the instructions comprising:
 (a) instructions for selecting a potential data carrier from within the downstream band; 
 (b) instructions for determining that the potential data carrier does not contain a signal modulated according to a first modulation scheme wherein the first modulation scheme is not a default modulation scheme used on signals in the downstream band; and 
 (c) instructions for determining that the potential data carrier contains a signal modulated according to a second modulation scheme wherein the second modulation scheme is the default modulation scheme used on signals in the downstream band by concluding that the potential data carrier contains a signal that is apparently not modulated according to the first modulation scheme. 
 
 
   
   
     43. A method for handling a plurality of modulation schemes for a downstream channel in a cable plant, comprising:
 (a) determining whether the downstream channel employs a modulation scheme that is not default for the downstream channel; and 
 (b) if the downstream channel is found to employ the modulation scheme that is not default, moving to a second downstream channel for analysis. 
 
   
   
     44. The method of  claim 43  further comprising:
 determining that the second downstream channel does not employ the non-default modulation scheme; and 
 determining whether the second downstream channel employs a default modulation scheme. 
 
   
   
     45. The method of  claim 44  wherein it is found that the second downstream channel employs the default modulation scheme, and further comprising determining whether a signal-to-noise ratio for the default modulation scheme in the second channel is greater than a threshold signal-to-noise ratio. 
   
   
     46. The method of  claim 45  wherein it is found that the signal-to-noise ratio for the default modulation scheme in the second channel is greater than the threshold signal-to-noise ratio, and further comprising selecting the second downstream channel for communication with a CMTS of the cable plant. 
   
   
     47. The cable modem of  claim 44  wherein it is found that the second downstream channel employs the default modulation scheme, and wherein the instructions further comprises instructions for determining whether a signal-to-noise ratio for the default modulation scheme in the second channel is greater than a threshold signal-to-noise ratio. 
   
   
     48. The cable modem of  claim 45  wherein it is found that the signal-to-noise ratio for the default modulation scheme in the second channel is greater than the threshold signal-to-noise ratio, and wherein the instructions further comprises instructions for selecting the second downstream channel for communication with a CMTS of the cable plant. 
   
   
     49. A system for handling a plurality of modulation schemes for a downstream channel in a cable plant, comprising:
 (a) means for determining whether the downstream channel employs a modulation scheme that is not default for the downstream channel; and 
 (b) means for moving to a second downstream channel for analysis. 
 
   
   
     50. The system of  claim 49  further comprising:
 means for determining that the second downstream channel does not employ the non-default modulation scheme; and 
 means for determining whether the second downstream channel employs a default modulation scheme. 
 
   
   
     51. The system of  claim 50  wherein it is found that the second downstream channel employs the default modulation scheme, and further comprising means for determining whether a signal-to-noise ratio for the default modulation scheme in the second channel is greater than a threshold signal-to-noise ratio. 
   
   
     52. The system of  claim 51  wherein it is found that the signal-to-noise ratio for the default modulation scheme in the second channel is greater than the threshold signal-to-noise ratio, and further comprising means for selecting the second downstream channel for communication with a CMTS of the cable plant. 
   
   
     53. A cable modem comprising:
 a CPU (central processing unit); 
 a memory; and 
 instructions for handling a plurality of modulation schemes for a downstream channel in a cable plant, the instructions comprising:
 (a) instructions for determining whether the downstream channel employs a modulation scheme that is not default for the downstream channel; and 
 (b) instructions for moving to a second downstream channel for analysis. 
 
 
   
   
     54. The cable modem of  claim 53  further comprising:
 instructions for determining that the second downstream channel does not employ the non-default modulation scheme; and 
 instructions for determining whether the second downstream channel employs a default modulation scheme.